Lithographic apparatus and device manufacturing method for writing a digital image

ABSTRACT

First pluralities of radiation spots generated by an array of individually controllable elements are exposed on a substrate. The radiation spots are equally spaced across an entire area of the substrate to be exposed. The substrate is then shifted relative to the array of individually controllable elements in a direction perpendicular to a scanning direction of the substrate. Second pluralities of radiation spots generated by the array of individually controllable elements are alternatingly formed on the substrate with respect to each of the first plurality of spots.

BACKGROUND

1. Field

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device.

2. Related Art

A lithographic apparatus is a machine that applies a desired patternonto a substrate or part of a substrate. A lithographic apparatus can beused, for example, in the manufacture of flat panel displays, integratedcircuits (ICs) and other devices involving fine structures. In aconventional apparatus, a patterning device, which can be referred to asa mask or a reticle, can be used to generate a circuit patterncorresponding to an individual layer of a flat panel display (or otherdevice). This pattern can be transferred on (part of) the substrate(e.g., a glass plate), e.g., via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate.

Instead of a circuit pattern, the patterning means can be used togenerate other patterns, for example a color filter pattern or a matrixof dots. Instead of a mask, the patterning device can comprise apatterning array that comprises an array of individually controllableelements. The pattern can be changed more quickly and for less cost insuch a system compared to a mask-based system.

A flat panel display substrate is typically rectangular in shape.Lithographic apparatus designed to expose a substrate of this type canprovide an exposure region that covers a full width of the rectangularsubstrate, or which covers a portion of the width (for example half ofthe width). The substrate can be scanned underneath the exposure region,while the mask or reticle is synchronously scanned through theprojection beam. In this way, the pattern is transferred to thesubstrate. If the exposure region covers the full width of the substratethen exposure can be completed with a single scan. If the exposureregion covers, for example, half of the width of the substrate, then thesubstrate can be moved transversely after the first scan, and a furtherscan is typically performed to expose the remainder of the substrate.

When using a print head comprising an array of individually controllableelements, the print head may not extend across an entire width of thesubstrate. Thus, several print heads are used or the substrate isshifted relative to the print head once exposure of a first area hasbeen completed. Furthermore, the pitch between individually controllableelements used in the print head can be much larger than the requiredpitch between spots exposed on the substrate. It can be difficult to fitsufficient print heads into the limited space available, so generally acombination of these two methods is used and the substrate is shiftedrelative to the plurality of print heads. However, the alignment ofprint heads with respect to each other may not be completely accurate.Furthermore, the shift of the substrate may not be exactly correct.

Both of these lead to so-called stitching errors due to the misalignmentof printed pixels in the exposed areas. Although steps can be taken toreduce stitching errors, these all occur in the same area where theexposures from a first exposure by a first print head overlap with anyother exposures. The spatial frequency of these areas of stitching canbe visible to the human eye, thus reducing the image quality.

Therefore, what is needed is a system and method of exposing thesubstrates using arrays of individually controllable elements in whichthe effect of stitching is minimized.

SUMMARY

According to one embodiment of the invention, there is provided a devicemanufacturing method comprising the following steps. Modulating thecross-section of a radiation beam using a patterning array ofindividually controllable elements. Projecting a plurality of radiationspots onto a substrate to generate a first plurality of spot exposuresusing a first patterning array of individually controllable elements.Scanning the substrate in a first direction, while projecting theplurality of spots. Projecting a plurality of radiation spots onto asubstrate to generate a second plurality of spot exposures using asecond patterning array of individually controllable elements.Alternating each of the second plurality of spot exposures with each ofthe first plurality of spot exposures in a second directionperpendicular to the first direction.

According to another embodiment of the invention, there is provided adevice manufacturing method comprising the following steps. Modulatingthe cross-section of a radiation beam using a patterning array ofindividually controllable elements. Projecting a plurality of radiationspots onto a substrate to generate a first plurality of spot exposures.Scanning the substrate in a first direction, while projecting theplurality of spots. Shifting the substrate relative to the patterningarray of individually controllable elements in a second directionperpendicular to the first direction. Projecting a plurality ofradiation spots onto a substrate to generate a second plurality of spotexposures. Alternating each of the second plurality of spot exposureswith the first plurality of spot exposures in the second direction.

Alternatively, an embodiment of the invention there is provided a devicemanufacturing method comprising the following steps. Modulating thecross-section of a radiation beam using a patterning array ofindividually controllable elements. Projecting a plurality of radiationspots onto a substrate to generate a first plurality of spot exposuresusing a first patterning array of individually controllable elements.Scanning the substrate in a first direction, while projecting theplurality of spots. Projecting a plurality of radiation spots onto asubstrate to generate a second plurality of spot exposures using asecond patterning array of individually controllable elements.Alternating each of the second plurality of spot exposures with each ofthe first plurality of spot exposures in the first direction.

According to another embodiment of the invention there is provided adevice manufacturing method comprising the following steps. Modulatingthe cross-section of a radiation beam using a patterning array ofindividually controllable elements. Projecting a plurality of radiationspots onto a substrate to generate a first plurality of spot exposures.Scanning the substrate in a first direction, while projecting theplurality of spots. Shifting the substrate relative to the patterningarray of individually controllable elements in a second directionperpendicular to the first direction. Projecting a plurality ofradiation spots onto a substrate to generate a second plurality of spotexposures. Alternating each of the second plurality of spot exposureswith the first plurality of spot exposures in the first direction.

According to a further embodiment of the invention there is provided alithographic projection apparatus comprising a first patterning array ofindividually controllable elements and a second patterning array ofindividually controllable elements located in a first direction relativeto the first patterning array. The second patterning array is arrangedsuch that the spot exposures generated by the second patterning arrayalternate with each of the spot exposure generated by the firstpatterning array in a second direction perpendicular to the firstdirection.

According to still another embodiment of the invention there is provideda lithographic projection apparatus comprising a patterning array ofindividually controllable elements, a shifting device, and a controller.The patterning array of individually controllable elements exposes afirst plurality of spot exposures on a substrate. The shifting devicemoves the substrate relative to the array of individually controllableelements in a second direction. The controller controls the shiftingdevice to shift the substrate relative to the patterning array, suchthat each of a second plurality of spot exposures exposed by an array ofindividually controllable elements is arranged between each of the firstplurality of spot exposures in the second direction.

According to yet another embodiment of the invention there is provided alithographic projection apparatus comprising a first patterning array ofindividually controllable elements and a second patterning array ofindividually controllable elements, which are located in a firstdirection relative to the first patterning array. The second patterningarray is arranged such that the spot exposures generated by the secondpatterning array alternate with each of the spot exposure generated bythe first patterning array in the first direction.

According to a still further embodiment of the invention there isprovided a lithographic projection apparatus comprising a patterningarray of individually controllable elements, a shifting device, and acontroller. The patterning array of individually controllable elementsexposes a first plurality of spot exposures on a substrate. The shiftingdevice moves the substrate relative to the array of individuallycontrollable elements in a second direction. The controller controls theshifting device to shift the substrate relative to the patterning array,such that each of a second plurality of spot exposures exposed by anarray of individually controllable elements is arranged between each ofthe first plurality of spot exposures in a first direction perpendicularto the second direction.

Further embodiments, features, and advantages of the present inventions,as well as the structure and operation of the various embodiments of thepresent invention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate one or more embodiments of the presentinvention and, together with the description, further serve to explainthe principles of the invention and to enable a person skilled in thepertinent art to make and use the invention.

FIGS. 1 and 2 depict lithographic apparatus, according to variousembodiments of the present invention.

FIG. 3 depicts a mode of transferring a pattern to a substrate using anembodiment of the invention as show in FIG. 2.

FIG. 4 depicts an arrangement of optical engines, according to oneembodiment of the present invention.

FIG. 5 shows the orientation of a print head relative to the directionof scanning of a substrate, according to one embodiment of the presentinvention.

FIGS. 6 a, 6 b, 7 a, 7 b, 8 a, 8 b, 8 c, 9 and 10 shows exposures,according to various embodiments of the present invention.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers canindicate identical or functionally similar elements. Additionally, theleft-most digit(s) of a reference number can identify the drawing inwhich the reference number first appears.

DETAILED DESCRIPTION

While specific configurations and arrangements are discussed, it shouldbe understood that this is done for illustrative purposes only. A personskilled in the pertinent art will recognize that other configurationsand arrangements can be used without departing from the spirit and scopeof the present invention. It will be apparent to a person skilled in thepertinent art that this invention can also be employed in a variety ofother applications.

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises an illuminationsystem IL, a patterning device PD, a substrate table WT, and aprojection system PS. The illumination system (illuminator) IL isconfigured to condition a radiation beam B (e.g., UV radiation).

The patterning device PD (e.g., a reticle or mask or an array ofindividually controllable elements) modulates the projection beam. Ingeneral, the position of the array of individually controllable elementswill be fixed relative to the projection system PS. However, it caninstead be connected to a positioner configured to accurately positionthe array of individually controllable elements in accordance withcertain parameters.

The substrate table WT is constructed to support a substrate (e.g., aresist-coated substrate) W and connected to a positioner PW configuredto accurately position the substrate in accordance with certainparameters.

The projection system (e.g., a refractive projection lens system) PS isconfigured to project the beam of radiation modulated by the array ofindividually controllable elements onto a target portion C (e.g.,comprising one or more dies) of the substrate W.

The illumination system can include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The term “patterning device” or “contrast device” used herein should bebroadly interpreted as referring to any device that can be used tomodulate the cross-section of a radiation beam, such as to create apattern in a target portion of the substrate. The devices can be eitherstatic patterning devices (e.g., masks or reticles) or dynamic (e.g.,arrays of programmable elements) patterning devices. For brevity, mostof the description will be in terms of a dynamic patterning device,however it is to be appreciated that a static pattern device can also beused without departing from the scope of the present invention.

It should be noted that the pattern imparted to the radiation beam maynot exactly correspond to the desired pattern in the target portion ofthe substrate, for example if the pattern includes phase-shiftingfeatures or so called assist features. Similarly, the pattern eventuallygenerated on the substrate may not correspond to the pattern formed atany one instant on the array of individually controllable elements. Thiscan be the case in an arrangement in which the eventual pattern formedon each part of the substrate is built up over a given period of time ora given number of exposures during which the pattern on the array ofindividually controllable elements and/or the relative position of thesubstrate changes.

Generally, the pattern created on the target portion of the substratewill correspond to a particular functional layer in a device beingcreated in the target portion, such as an integrated circuit or a flatpanel display (e.g., a color filter layer in a flat panel display or athin film transistor layer in a flat panel display). Examples of suchpatterning devices include, e.g., reticles, programmable mirror arrays,laser diode arrays, light emitting diode arrays, grating light valves,and LCD arrays.

Patterning devices whose pattern is programmable with the aid ofelectronic means (e.g., a computer), such as patterning devicescomprising a plurality of programmable elements (e.g., all the devicesmentioned in the previous sentence except for the reticle), arecollectively referred to herein as “contrast devices.” In one example,the patterning device comprises at least 10 programmable elements, e.g.,at least 100,at least 1000,at least 10000,at least 100000,at least1000000,or at least 10000000 programmable elements.

A programmable mirror array can comprise a matrix-addressable surfacehaving a viscoelastic control layer and a reflective surface. The basicprinciple behind such an apparatus is that, e.g., addressed areas of thereflective surface reflect incident light as diffracted light, whereasunaddressed areas reflect incident light as undiffracted light. Using anappropriate spatial filter, the undiffracted light can be filtered outof the reflected beam, leaving only the diffracted light to reach thesubstrate. In this manner, the beam becomes patterned according to theaddressing pattern of the matrix-addressable surface.

It will be appreciated that, as an alternative, the filter can filterout the diffracted light, leaving the undiffracted light to reach thesubstrate.

An array of diffractive optical MEMS devices (micro-electro-mechanicalsystem devices) can also be used in a corresponding manner. In oneexample, a diffractive optical MEMS device is comprised of a pluralityof reflective ribbons that can be deformed relative to one another toform a grating that reflects incident light as diffracted light.

A further alternative example of a programmable mirror array employs amatrix arrangement of tiny mirrors, each of which can be individuallytilted about an axis by applying a suitable localized electric field, orby employing piezoelectric actuation means. Once again, the mirrors arematrix-addressable, such that addressed mirrors reflect an incomingradiation beam in a different direction to unaddressed mirrors; in thismanner, the reflected beam can be patterned according to the addressingpattern of the matrix-addressable mirrors. The required matrixaddressing can be performed using suitable electronic means.

Another example PD is a programmable LCD array.

The lithographic apparatus can comprise one or more contrast devices.For example, it can have a plurality of arrays of individuallycontrollable elements, each controlled independently of each other. Insuch an arrangement, some or all of the arrays of individuallycontrollable elements can have at least one of a common illuminationsystem (or part of an illumination system), a common support structurefor the arrays of individually controllable elements, and/or a commonprojection system (or part of the projection system).

In an example, such as the embodiment depicted in FIG. 1, the substrateW has a substantially circular shape, optionally with a notch and/or aflattened edge along part of its perimeter. In an example, the substratehas a polygonal shape, e.g., a rectangular shape.

In example where the substrate has a substantially circular shapeinclude examples where the substrate has a diameter of at least 25 mm,for instance at least 50 mm, at least 75 mm, at least 100 mm, at least125 mm, at least 150 mm, at least 175 mm, at least 200 mm, at least 250mm, or at least 300 mm. In an embodiment, the substrate has a diameterof at most 500 mm, at most 400 mm, at most 350 mm, at most 300 mm, atmost 250 mm, at most 200 mm, at most 150 mm, at most 100 mm, or at most75 mm.

In examples where the substrate is polygonal, e.g., rectangular, includeexamples where at least one side, e.g., at least 2 sides or at least 3sides, of the substrate has a length of at least 5 cm, e.g., at least 25cm, at least 50 cm, at least 100 cm, at least 150 cm, at least 200 cm,or at least 250 cm.

In one example, at least one side of the substrate has a length of atmost 1000 cm, e.g., at most 750 cm, at most 500 cm, at most 350 cm, atmost 250 cm, at most 150 cm, or at most 75 cm.

In one example, the substrate W is a wafer, for instance a semiconductorwafer. In one example, the wafer material is selected from the groupconsisting of Si, SiGe, SiGeC, SiC, Ge, GaAs, InP, and InAs. In oneexample, the wafer is a III/V compound semiconductor wafer. In oneexample, the wafer is a silicon wafer. In an embodiment, the substrateis a ceramic substrate. In one example, the substrate is a glasssubstrate. In one example, the substrate is a plastic substrate. In oneexample, the substrate is transparent (for the naked human eye). In oneexample, the substrate is colored. In one example, the substrate isabsent a color.

The thickness of the substrate can vary and, to an extent, can depend,e.g., on the substrate material and/or the substrate dimensions. In oneexample, the thickness is at least 50 μm, e.g., at least 100 μm, atleast 200 μm, at least 300 μm, at least 400 μm, at least 500 μm, or atleast 600 μm. In one example, the thickness of the substrate is at most5000 μm, e.g., at most 3500 μm, at most 2500 μm, at most 1750 μm, atmost 1250 μm, at most 1000 μm, at most 800 μm, at most 600 μm, at most500 μm, at most 400 μm, or at most 300 μm.

The substrate referred to herein can be processed, before or afterexposure, in for example a track (a tool that typically applies a layerof resist to a substrate and develops the exposed resist), a metrologytool, and/or an inspection tool. In one example, a resist layer isprovided on the substrate.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein can be considered as synonymous with the moregeneral term “projection system.”

The projection system can image the pattern on the array of individuallycontrollable elements, such that the pattern is coherently formed on thesubstrate. Alternatively, the projection system can image secondarysources for which the elements of the array of individually controllableelements act as shutters. In this respect, the projection system cancomprise an array of focusing elements such as a micro lens array (knownas an MLA) or a Fresnel lens array, e.g., to form the secondary sourcesand to image spots onto the substrate. In one example, the array offocusing elements (e.g., MLA) comprises at least 10 focus elements,e.g., at least 100 focus elements, at least 1000 focus elements, atleast 10000 focus elements, at least 100000 focus elements, or at least1000000 focus elements. In one example, the number of individuallycontrollable elements in the patterning device is equal to or greaterthan the number of focusing elements in the array of focusing elements.In one example, one or more (e.g., 1000 or more, the majority, or abouteach) of the focusing elements in the array of focusing elements can beoptically associated with one or more of the individually controllableelements in the array of individually controllable elements, e.g., with2 or more of the individually controllable elements in the array ofindividually controllable elements, such as 3 or more, 5 or more, 10 ormore, 20 or more, 25 or more, 35 or more, or 50 or more. In one example,the MLA is movable (e.g., with the use of actuators) at least in thedirection to and away from the substrate, e.g., with the use of one ormore actuators. Being able to move the MLA to and away from thesubstrate allows, e.g., for focus adjustment without having to move thesubstrate.

As herein depicted in FIGS. 1 and 2, the apparatus is of a reflectivetype (e.g., employing a reflective array of individually controllableelements). Alternatively, the apparatus can be of a transmissive type(e.g., employing a transmissive array of individually controllableelements).

The lithographic apparatus can be of a type having two (dual stage) ormore substrate tables. In such “multiple stage” machines, the additionaltables can be used in parallel, or preparatory steps can be carried outon one or more tables while one or more other tables are being used forexposure.

The lithographic apparatus can also be of a type wherein at least aportion of the substrate can be covered by an “immersion liquid” havinga relatively high refractive index, e.g., water, so as to fill a spacebetween the projection system and the substrate. An immersion liquid canalso be applied to other spaces in the lithographic apparatus, forexample, between the patterning device and the projection system.Immersion techniques are well known in the art for increasing thenumerical aperture of projection systems. The term “immersion” as usedherein does not mean that a structure, such as a substrate, must besubmerged in liquid, but rather only means that liquid is locatedbetween the projection system and the substrate during exposure.

Referring again to FIG. 1, the illuminator IL receives a radiation beamfrom a radiation source SO. In one example, the radiation sourceprovides radiation having a wavelength of at least 5 nm, e.g., at least10 nm, at least 50 nm, at least 100 nm, at least 150 nm, at least 175nm, at least 200 nm, at least 250 nm, at least 275 nm, at least 300 nm,at least 325 nm, at least 350 nm, or at least 360 nm. In one example,the radiation provided by radiation source SO has a wavelength of atmost 450 nm, e.g., at most 425 nm, at most 375 nm, at most 360 nm, atmost 325 nm, at most 275 nm, at most 250 nm, at most 225 nm, at most 200nm, or at most 175 nm. In one example, the radiation has a wavelengthincluding 436 nm, 405 nm, 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, and/or126 nm. In one example, the radiation includes a wavelength of around365 nm or around 355 nm. In one example, the radiation includes a broadband of wavelengths, for example encompassing 365, 405,and 436 nm. A 355nm laser source could be used. The source and the lithographic apparatuscan be separate entities, for example when the source is an excimerlaser. In such cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source can be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, can be referred to as a radiation system.

The illuminator IL, can comprise an adjuster AD for adjusting theangular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator can be adjusted. In addition, theilluminator IL can comprise various other components, such as anintegrator IN and a condenser CO. The illuminator can be used tocondition the radiation beam to have a desired uniformity and intensitydistribution in its cross-section. The illuminator IL, or an additionalcomponent associated with it, can also be arranged to divide theradiation beam into a plurality of sub-beams that can, for example, eachbe associated with one or a plurality of the individually controllableelements of the array of individually controllable elements. Atwo-dimensional diffraction grating can, for example, be used to dividethe radiation beam into sub-beams. In the present description, the terms“beam of radiation” and “radiation beam” encompass, but are not limitedto, the situation in which the beam is comprised of a plurality of suchsub-beams of radiation.

The radiation beam B is incident on the patterning device PD (e.g., anarray of individually controllable elements) and is modulated by thepatterning device. Having been reflected by the patterning device PD,the radiation beam B passes through the projection system PS, whichfocuses the beam onto a target portion C of the substrate W. With theaid of the positioner PW and position sensor IF2 (e.g., aninterferometric device, linear encoder, capacitive sensor, or the like),the substrate table WT can be moved accurately, e.g., so as to positiondifferent target portions C in the path of the radiation beam B. Whereused, the positioning means for the array of individually controllableelements can be used to correct accurately the position of thepatterning device PD with respect to the path of the beam B, e.g.,during a scan.

In one example, movement of the substrate table WT is realized with theaid of a long-stroke module (course positioning) and a short-strokemodule (fine positioning), which are not explicitly depicted in FIG. 1.In one example, the apparatus is absent at least a short stroke modulefor moving substrate table WT. A similar system can also be used toposition the array of individually controllable elements. It will beappreciated that the projection beam B can alternatively/additionally bemoveable, while the object table and/or the array of individuallycontrollable elements can have a fixed position to provide the requiredrelative movement. Such an arrangement can assist in limiting the sizeof the apparatus. As a further alternative, which can, e.g., beapplicable in the manufacture of flat panel displays, the position ofthe substrate table WT and the projection system PS can be fixed and thesubstrate W can be arranged to be moved relative to the substrate tableWT. For example, the substrate table WT can be provided with a systemfor scanning the substrate W across it at a substantially constantvelocity.

As shown in FIG. 1, the beam of radiation B can be directed to thepatterning device PD by means of a beam splitter BS configured such thatthe radiation is initially reflected by the beam splitter and directedto the patterning device PD. It should be realized that the beam ofradiation B can also be directed at the patterning device without theuse of a beam splitter. In one example, the beam of radiation isdirected at the patterning device at an angle between 0 and 90°, e.g.,between 5 and 85°, between 15 and 75°, between 25 and 65°, or between 35and 55° (the embodiment shown in FIG. 1 is at a 90° angle). Thepatterning device PD modulates the beam of radiation B and reflects itback to the beam splitter BS which transmits the modulated beam to theprojection system PS. It will be appreciated, however, that alternativearrangements can be used to direct the beam of radiation B to thepatterning device PD and subsequently to the projection system PS. Inparticular, an arrangement such as is shown in FIG. 1 may not berequired if a transmissive patterning device is used.

The depicted apparatus can be used in several modes:

1. In step mode, the array of individually controllable elements and thesubstrate are kept essentially stationary, while an entire patternimparted to the radiation beam is projected onto a target portion C atone go (i.e., a single static exposure). The substrate table WT is thenshifted in the X and/or Y direction so that a different target portion Ccan be exposed. In step mode, the maximum size of the exposure fieldlimits the size of the target portion C imaged in a single staticexposure.

2. In scan mode, the array of individually controllable elements and thesubstrate are scanned synchronously while a pattern imparted to theradiation beam is projected onto a target portion C (i.e., a singledynamic exposure). The velocity and direction of the substrate relativeto the array of individually controllable elements can be determined bythe (de-) magnification and image reversal characteristics of theprojection system PS. In scan mode, the maximum size of the exposurefield limits the width (in the non-scanning direction) of the targetportion in a single dynamic exposure, whereas the length of the scanningmotion determines the height (in the scanning direction) of the targetportion.

3. In pulse mode, the array of individually controllable elements iskept essentially stationary and the entire pattern is projected onto atarget portion C of the substrate W using a pulsed radiation source. Thesubstrate table WT is moved with an essentially constant speed such thatthe projection beam B is caused to scan a line across the substrate W.The pattern on the array of individually controllable elements isupdated as required between pulses of the radiation system and thepulses are timed such that successive target portions C are exposed atthe required locations on the substrate W. Consequently, the projectionbeam B can scan across the substrate W to expose the complete patternfor a strip of the substrate. The process is repeated until the completesubstrate W has been exposed line by line.

4. In continuous scan mode, essentially the same as pulse mode exceptthat the substrate W is scanned relative to the modulated beam ofradiation B at a substantially constant speed and the pattern on thearray of individually controllable elements is updated as the projectionbeam B scans across the substrate W and exposes it. A substantiallyconstant radiation source or a pulsed radiation source, synchronized tothe updating of the pattern on the array of individually controllableelements, can be used.

5. In pixel grid imaging mode, which can be performed using thelithographic apparatus of FIG. 2, the pattern formed on substrate W isrealized by subsequent exposure of spots formed by a spot generator thatare directed onto patterning device PD. The exposed spots havesubstantially the same shape. On substrate W the spots are printed insubstantially a grid. In one example, the spot size is larger than apitch of a printed pixel grid, but much smaller than the exposure spotgrid. By varying intensity of the spots printed, a pattern is realized.In between the exposure flashes the intensity distribution over thespots is varied.

Combinations and/or variations on the above described modes of use orentirely different modes of use can also be employed.

In lithography, a pattern is exposed on a layer of resist on thesubstrate. The resist is then developed. Subsequently, additionalprocessing steps are performed on the substrate. The effect of thesesubsequent processing steps on each portion of the substrate depends onthe exposure of the resist. In particular, the processes are tuned suchthat portions of the substrate that receive a radiation dose above agiven dose threshold respond differently to portions of the substratethat receive a radiation dose below the dose threshold. For example, inan etching process, areas of the substrate that receive a radiation doseabove the threshold are protected from etching by a layer of developedresist. However, in the post-exposure development, the portions of theresist that receive a radiation dose below the threshold are removed andtherefore those areas are not protected from etching. Accordingly, adesired pattern can be etched. In particular, the individuallycontrollable elements in the patterning device are set such that theradiation that is transmitted to an area on the substrate within apattern feature is at a sufficiently high intensity that the areareceives a dose of radiation above the dose threshold during theexposure. The remaining areas on the substrate receive a radiation dosebelow the dose threshold by setting the corresponding individuallycontrollable elements to provide a zero or significantly lower radiationintensity.

In practice, the radiation dose at the edges of a pattern feature doesnot abruptly change from a given maximum dose to zero dose even if theindividually controllable elements are set to provide the maximumradiation intensity on one side of the feature boundary and the minimumradiation intensity on the other side. Instead, due to diffractiveeffects, the level of the radiation dose drops off across a transitionzone. The position of the boundary of the pattern feature ultimatelyformed by the developed resist is determined by the position at whichthe received dose drops below the radiation dose threshold. The profileof the drop-off of radiation dose across the transition zone, and hencethe precise position of the pattern feature boundary, can be controlledmore precisely by setting the individually controllable elements thatprovide radiation to points on the substrate that are on or near thepattern feature boundary not only to maximum or minimum intensity levelsbut also to intensity levels between the maximum and minimum intensitylevels. This is commonly referred to as “grayscaling.”

Grayscaling provides greater control of the position of the patternfeature boundaries than is possible in a lithography system in which theradiation intensity provided to the substrate by a given individuallycontrollable element can only be set to two values (namely just amaximum value and a minimum value). In an embodiment, at least threedifferent radiation intensity values can be projected onto thesubstrate, e.g., at least 4 radiation intensity values, at least 8radiation intensity values, at least 16 radiation intensity values, atleast 32 radiation intensity values, at least 64 radiation intensityvalues, at least 128 radiation intensity values, or at least 256radiation intensity values.

It should be appreciated that grayscaling can be used for additional oralternative purposes to that described above. For example, theprocessing of the substrate after the exposure can be tuned, such thatthere are more than two potential responses of regions of the substrate,dependent on received radiation dose level. For example, a portion ofthe substrate receiving a radiation dose below a first thresholdresponds in a first manner; a portion of the substrate receiving aradiation dose above the first threshold but below a second thresholdresponds in a second manner; and a portion of the substrate receiving aradiation dose above the second threshold responds in a third manner.Accordingly, grayscaling can be used to provide a radiation dose profileacross the substrate having more than two desired dose levels. In anembodiment, the radiation dose profile has at least 2 desired doselevels, e.g., at least 3 desired radiation dose levels, at least 4desired radiation dose levels, at least 6 desired radiation dose levelsor at least 8 desired radiation dose levels.

It should further be appreciated that the radiation dose profile can becontrolled by methods other than by merely controlling the intensity ofthe radiation received at each point on the substrate, as describedabove. For example, the radiation dose received by each point on thesubstrate can alternatively or additionally be controlled by controllingthe duration of the exposure of the point. As a further example, eachpoint on the substrate can potentially receive radiation in a pluralityof successive exposures. The radiation dose received by each point can,therefore, be alternatively or additionally controlled by exposing thepoint using a selected subset of the plurality of successive exposures.

In order to form the required pattern on the substrate, it is necessaryto set each of the individually controllable elements in the patterningdevice to the requisite state at each stage during the exposure process.Therefore, control signals, representing the requisite states, must betransmitted to each of the individually controllable elements. In oneexample, the lithographic apparatus includes a controller that generatesthe control signals. The pattern to be formed on the substrate can beprovided to the lithographic apparatus in a vector-defined format, suchas GDSII. In order to convert the design information into the controlsignals for each individually controllable element, the controllerincludes one or more data manipulation devices, each configured toperform a processing step on a data stream that represents the pattern.The data manipulation devices can collectively be referred to as the“datapath.”

The data manipulation devices of the datapath can be configured toperform one or more of the following functions: converting vector-baseddesign information into bitmap pattern data; converting bitmap patterndata into a required radiation dose map (namely a required radiationdose profile across the substrate); converting a required radiation dosemap into required radiation intensity values for each individuallycontrollable element; and converting the required radiation intensityvalues for each individually controllable element into correspondingcontrol signals.

FIG. 2 depicts an arrangement of the apparatus according to the presentinvention that can be used, e.g., in the manufacture of flat paneldisplays. Components corresponding to those shown in FIG. 1 are depictedwith the same reference numerals. Also, the above descriptions of thevarious embodiments, e.g., the various configurations of the substrate,the contrast device, the MLA, the beam of radiation, etc., remainapplicable.

FIG. 2 depicts an arrangement of a lithographic apparatus, according toone embodiment of the present invention. This embodiment can be used,e.g., in the manufacture of flat panel displays. Componentscorresponding to those shown in FIG. 1 are depicted with the samereference numerals. Also, the above descriptions of the variousembodiments, e.g., the various configurations of the substrate, thecontrast device, the MLA, the beam of radiation, etc., remainapplicable.

As shown in FIG. 2, the projection system PS includes a beam expander,which comprises two lenses L1, L2. The first lens L1 is arranged toreceive the modulated radiation beam B and focus it through an aperturein an aperture stop AS. A further lens AL can be located in theaperture. The radiation beam B then diverges and is focused by thesecond lens L2 (e.g., a field lens).

The projection system PS further comprises an array of lenses MLAarranged to receive the expanded modulated radiation B. Differentportions of the modulated radiation beam B, corresponding to one or moreof the individually controllable elements in the patterning device PD,pass through respective different lenses in the array of lenses MLA.Each lens focuses the respective portion of the modulated radiation beamB to a point which lies on the substrate W. In this way an array ofradiation spots S is exposed onto the substrate W. It will beappreciated that, although only eight lenses of the illustrated array oflenses 14 are shown, the array of lenses can comprise many thousands oflenses (the same is true of the array of individually controllableelements used as the patterning device PD).

FIG. 3 illustrates schematically how a pattern on a substrate W isgenerated using the system of FIG. 2, according to one embodiment of thepresent invention. The filled in circles represent the array of spots Sprojected onto the substrate W by the array of lenses MLA in theprojection system PS. The substrate W is moved relative to theprojection system PS in the Y direction as a series of exposures areexposed on the substrate W. The open circles represent spot exposures SEthat have previously been exposed on the substrate W. As shown, eachspot projected onto the substrate by the array of lenses within theprojection system PS exposes a row R of spot exposures on the substrateW. The complete pattern for the substrate is generated by the sum of allthe rows R of spot exposures SE exposed by each of the spots S. Such anarrangement is commonly referred to as “pixel grid imaging,” discussedabove.

It can be seen that the array of radiation spots S is arranged at anangle θ relative to the substrate W (the edges of the substrate lieparallel to the X and Y directions). This is done so that when thesubstrate is moved in the scanning direction (the Y-direction), eachradiation spot will pass over a different area of the substrate, therebyallowing the entire substrate to be covered by the array of radiationspots 15. In one example, the angle θ is at most 20°, 10°, e.g., at most5°, at most 3°, at most 1°, at most 0.5°, at most 0.25°, at most 0.10°,at most 0.05°, or at most 0.01°. In one example, the angle θ is at least0.001°.

FIG. 4 shows schematically how an entire flat panel display substrate Wcan be exposed in a single scan using a plurality of optical engines,according to one embodiment of the present invention. In the exampleshown eight arrays SA of radiation spots S are produced by eight opticalengines (not shown), arranged in two rows R1, R2 in a “chess board”configuration, such that the edge of one array of radiation spots Sslightly overlaps (in the scanning direction Y) with the edge of theadjacent array of radiation spots. In one example, the optical enginesare arranged in at least 3 rows, for instance 4 rows or 5 rows. In thisway, a band of radiation extends across the width of the substrate W,allowing exposure of the entire substrate to be performed in a singlescan. It will be appreciated that any suitable number of optical enginescan be used. In one example, the number of optical engines is at least1,e.g., at least 2,at least 4,at least 8,at least 10,at least 12,atleast 14,or at least 17.In one example, the number of optical engines isless than 40,e.g., less than 30 or less than 20.

Each optical engine can comprise a separate illumination system IL,patterning device PD and projection system PS as described above. It isto be appreciated, however, that two or more optical engines can shareat least a part of one or more of the illumination system, patterningdevice and projection system.

FIG. 5 shows an orientation of a print head PH at an angle θ to a scandirection y, according to one embodiment of the present invention. Inthis orientation, the array of individually controllable elements isoriented at an angle θ to the scan direction, y. θ is chosen such thatevery nth line is printed, where n >1.

A print head in a lithographic apparatus is a part of the apparatus inwhich a pattern is applied to part or all of a beam of radiation that isprojected onto the substrate. The print head may comprise an array ofindividually controllable elements or a plurality of arrays ofindividually controllable elements, mounted on a common support. Theprint head may also include some or all of the components of theprojection system, for example. If the print head has a plurality ofarrays of individually controllable elements, some or all of thecomponents of the projection system may be common for all of the arraysof individually controllable elements. Some or all of the components ofthe projection system, however, maybe used in conjunction with one ofthe arrays of individually controllable elements. It will be appreciatedthat the print head may include additional components.

FIGS. 6 a, 6 b, 7 a, 7 b, 8 a, 8 b, and 8 c shows exposures, accordingto various embodiments of the present invention.

In FIG. 6 a a spot is printed in every second line. FIG. 6 a shows thespots, S, exposed on a substrate after a first exposure by three printheads. The exposures by the first print head are shown as hashed,exposures by a second print head are shown as crossed, and the exposuresby a third print head are shown as shaded. The substrate is then shiftedrelative to the print head (or the print head shifted relative to thesubstrate) in a direction perpendicular to the scanning direction.

A second exposure then takes place, as shown in FIG. 6 b, with each ofthe spots exposed during the second exposure alternating with the spotsexposed during the first exposure in a direction perpendicular to thescanning direction—this is so called “interlacing.” The errors resultingfrom the shift in the substrate position perpendicular to the scanningdirection are thus distributed across the width of the substrate ratherthan being confined to the stitching zone. The spatial frequency of thestitching errors is high, so they are less visible to the human eye.

Although described here using just the exposure of individual spots, inone example entire rows R of spots are generally exposed (as describedabove in conjunction with FIG. 3), followed by the second plurality ofspots (or rows), which can also comprise rows R of spots.

FIGS. 7 a and 7 b show a similar method in which the shift in thesubstrate between the first and second exposures is sufficiently large,such that the second exposures from the second print head are interlacedwith the first exposures from the first print head. This ensures thaterrors introduced into stitching zones as a result of misalignment ofneighboring print heads are interlaced across substrates.

FIGS. 6 a, 6 b, 7 a, and 7 b show arrangements in which the print headsare arranged to print every second line (n=2), whereas FIG. 8 a shows anarrangement in which each print head prints every third line (n=3). FIG.8 b shows spots exposed after the second exposure. With the print headarranged to print every third line, a third exposure is also needed tocomplete each line, and FIG. 8 c shows this. In other examples, theapparatus could also be arranged to print every fourth, fifth, sixth etcline.

As an alternative to shifting the substrate relative to the printingheads to generate the subsequent interlaced spots, an additional printhead or print heads could be arranged downstream in the scanningdirection, y. This is shown in FIG. 9 in which the first print head PH1exposes a first plurality of spots (shown as hashed). In FIG. 9, allpreviously exposed spots are also shown, in a similar manner to FIG. 3.A second print head PH2 then exposes a second plurality of spots (shownas crossed), each arranged between each of the first plurality of spotsin the x direction (perpendicular to the y scanning direction). It is tobe appreciated that, although only one print head is shown in the xdirection, in various examples there can be several print heads in the xdirection. Also, there could be more than two print heads in the ydirection.

Described above is interlacing in the x direction, but in other examplesinterlacing can also take place in the y direction either in additionto, or alternatively, to interlacing in the x direction.

FIG. 10 shows a first plurality of spots (shown as hashed) exposed by afirst print head PH1. Downstream in the scanning direction, y, is asecond print head PH2 which exposes a second plurality of spots (shownas crossed), each of the second plurality of spots arranged between eachof the first plurality of spots. Thus, as can be seen, the combinedeffect of the first and second spot exposures is to allow the entiresubstrate to be exposed. In this embodiment the timing of the exposuresof the first and second print heads, PH1 and PH2, respectively, must beaccurately controlled to ensure that the exposures are accuratelyinterlaced.

In one example, as an alternative to the embodiment shown in FIG. 10,all of the first plurality of spots are exposed by a print head orheads, the substrate W is then shifted relative to the print head orheads, such that the second plurality of spots, each arranged betweeneach of the first plurality of spots in the y direction, can be exposedby the same print head or heads. The relative shift between thesubstrate and the print head(s) can be in the y direction or acombination of the x and y directions.

Although specific reference can be made in this text to the use oflithographic apparatus in the manufacture of a specific device (e.g., anintegrated circuit or a flat panel display), it should be understoodthat the lithographic apparatus described herein can have otherapplications. Applications include, but are not limited to, themanufacture of integrated circuits, integrated optical systems, guidanceand detection patterns for magnetic domain memories, flat-paneldisplays, liquid-crystal displays (LCDs), thin-film magnetic heads,micro-electromechanical devices (MEMS), etc. Also, for instance in aflat panel display, the present apparatus can be used to assist in thecreation of a variety of layers, e.g., a thin film transistor layerand/or a color filter layer.

Although specific reference can have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention can be used in otherapplications, for example imprint lithography, where the context allows,and is not limited to optical lithography. In imprint lithographytopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device can be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

CONCLUSION

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.Thus, the breadth and scope of the present invention should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections can set forth one or more,but not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

1. A lithographic projection apparatus, comprising: a first patterningarray of individually controllable elements configured to generate afirst set of spot exposures during a first exposure of a substrate; anda second patterning array of individually controllable elements locatedin a first direction relative to the first patterning array configuredto generate a second set of spot exposures during a second exposure ofthe substrate, wherein the second patterning array is arranged such thateach spot exposure of the first set alternates with each spot exposureof the second set in a second direction perpendicular to the firstdirection, wherein the spot exposures of the first set are separatedfrom the spot exposures of the second set by at least one spot width. 2.The lithographic projection apparatus of claim 1, wherein the patterningarray is oriented at an angle that is greater than zero degrees withrespect to the first direction.
 3. The lithographic projection apparatusof claim 2, wherein the angle is such that there is an integer number ofspot widths in the second direction between consecutive spot exposuresin the first plurality of spot exposures.
 4. A lithographic projectionapparatus, comprising: a first patterning array of individuallycontrollable elements configured to generate a first set of spotexposures during a first exposure of a substrate; and a secondpatterning array of individually controllable elements located in afirst direction relative to the first patterning array configured togenerate a second set of spot exposures during a second exposure of thesubstrate, wherein the second patterning array is arranged such thatspot exposures of the first set alternate with spot exposures of thesecond set in the first direction, wherein the spot exposures generatedby the first patterning array are separated from the spot exposuresgenerated by the second patterning array by at least one spot width. 5.The lithographic projection apparatus of claim 4, wherein the patterningarray is oriented at an angle that is greater than zero degrees withrespect to the first direction.
 6. The lithographic projection apparatusof claim 5, wherein the angle is such that there is an integer number ofspot widths in the second direction between consecutive spot exposuresin the first plurality of spot exposures.